ITEM 308  Asphalt Treated Free Draining Base

308.01  Description

308.02  Materials

308.03  Composition

308.04  Design Verification

308.05  Preparation of Materials

308.06  Rollers

308.07  Weather Limitations

308.08  Spreading and Compacting

308.09  Thickness Tolerances

308.10  Surface Tolerance

308.11  Quality Control and Acceptance

308.12  Underdrains

308.13  Protection of the ATFDB

308.14  Exposure to the Elements

308.15  Method of Measurements

308.16  Basis of Payment


308.01  Description.  This work consists of constructing an asphalt treated free draining base (ATFDB) course, mixed in a central plant and spread and compacted on a prepared surface.

The requirements of Item 401 apply, except as modified by this specification.

308.02  Materials.  Furnish aggregate conforming to the gradation requirements of No. 67 or 57 aggregate as defined in Table 703.01-1 and consisting of a crushed carbonate stone, crushed gravel, or air cooled blast furnace slag conforming to the requirements of 703.04 for 301 asphalt concrete base, except provide aggregate with a maximum percentage of wear for the Los Angeles test of 40.  If using crushed gravel, ensure that 90 percent by count has at least two mechanically fractured faces conforming to the Pennsylvania Department of Transportation Test Method No. 621, Determining the Percentage of Crushed Fragments in Gravel.

Use PG 64-22 asphalt binder conforming to the requirements of 702.01.

Do not use reclaimed asphalt concrete pavement.

308.03  Composition.  Combine asphalt binder with the aggregate in an amount equal to 1.5 to 3.5 percent by weight of the mix.  After mixing with asphalt binder, ensure that the aggregate:

A.     Does not show excess drainage at 250 °F (120 °C).

B.      Is coated with shiny black coating of asphalt binder.  Minor bare aggregate exposure is acceptable.

C.      Is not brown or dull in appearance, a sign of excess aggregate absorption of the asphalt binder or low asphalt binder content.

308.04  Design Verification.  A minimum of 3 weeks before the production of the ATFDB, submit a computed blend of aggregate and asphalt binder, using standard JMF submittal forms, and production temperature range to the Laboratory for initial design verification.  Deliver to the Laboratory 1 gallon (4 L) of asphalt binder and one bag of aggregate.  Notify the Laboratory before the delivery of any material.

Final design verification is subject to field verification and actual performance.  Field verification may include additional testing by the Laboratory.

308.05  Preparation of Materials.  Mix the ATFDB material within the established temperature range and immediately load it into the trucks.

308.06  Rollers.  Use only tandem steel wheel rollers weighing 6 to 10 tons (5.5 to 9 metric tons) for compaction.

308.07  Weather Limitations.  Spread the ATFDB only when the atmospheric temperature is above 45 °F (7 °C).

Do not place the ATFDB when rain is imminent.  If rain occurs during placement of the ATFDB, cease all operations.  Do not place the ATFDB during any weather conditions that would cause its degradation, segregation, or contamination.

308.08  Spreading and Compacting.  Spread the ATFDB material in a method that produces a smooth, uniform layer before compacting.  Do not spread on frozen material.

Unless otherwise directed, when compacting the ATFDB material, make at least two roller passes over any given point on the surface.  Compact the ATFDB sufficiently to support the weight of the equipment that will place the next layer of pavement.  Do not overcompact the ATFDB to the extent the aggregate particles are crushed or broken.  Complete rolling before the mix temperature has dropped to less than 100 °F (38 °C).

Do not cool ATFDB with water.

Form transverse construction joints by cutting back into the completed work to form a vertical face.

If significant breakup of the ATFDB occurs at or near the outer portion of a lift during the compaction operation, provide lateral support using forms or other methods approved by the Engineer at no additional cost to the Department.  Do not contaminate the ATFDB with this lateral support.

When the ATFDB is placed in areas inaccessible to rollers, compact it using a method approved by the Engineer.

After compaction has been completed, do not place the next layer of pavement on the ATFDB until the next day.

308.09  Thickness Tolerances.  Make the compacted thickness of the ATFDB 4 inches (100 mm).  Ensure the placed ATFDB conforms to the specified thickness by randomly checking the thickness during construction.  Remove all sections found to be ±1/2 inch (±12 mm) from the specified thickness and replace them with ATFDB at no additional expense to the Department.

308.10  Surface Tolerance.  Ensure that the finished surface is uniform and varies no more than 1/2 inch (12 mm) from a 10-foot (3 m) straightedge applied to the surface parallel to the centerline of the pavement.  Remove any section found to be out of tolerance and replace it with ATFDB within the specified tolerance at no additional expense to the Department.

308.11  Quality Control and Acceptance.  The quality control and acceptance requirements of Item 403 apply, except as follows.

Each day before the start of production, obtain two separate samples of the aggregate stockpile and test the samples for gradation.  If both samples pass the gradation test, the Contractor may produce ATFDB all day.  If one or both of the samples fail the gradation test, do not begin production until the Department is satisfied that the stockpile conforms to requirements.  Record results on a TE-199.  If any material is added to the stockpile, immediately take another sample and test it.

The Department will base acceptance of the Contractor’s daily aggregate gradation test results on one Department stockpile verification sample from the asphalt plant aggregate stockpile taken and tested for each five days of production.  If the Department test shows the stockpile conforms to the appropriate requirements, the Department can accept material per the Contractor’s daily results.  If the Department test does not verify the stockpile condition, test aggregate according to Item 403 for the remainder of the project.

If testing according to Item 403, split each sample and retain half of it for Department verification.  The Department will randomly verify a Contractor gradation test once in every 5 production days.  If the Department verification test compares by ±3.0 percent on the No. 4 (4.75 mm) sieve and is not outside the gradation band, the Department will base acceptance on the Contractor’s test results.  The Department may verify using additional tests if desired.  If the Department test does not verify the Contractor’s results, the Department will base acceptance on the test results of one split sample for each day represented by the original verification sample.  Replace failed material in place unless otherwise directed by the District.

The Department will base acceptance of the asphalt binder content on the field inspection of the coating on the aggregate.  To be accepted, the ATFDB should be coated with shiny black coating of asphalt binder and not be brown or dull in appearance.  Minor inconsistent bare aggregate exposure is acceptable.  If the delivered mix is brown or dull in appearance, adjust the asphalt binder content to the satisfaction of the Engineer.

308.12  Underdrains.  Ensure that the underdrain system is functional before placing the ATFDB.

Do not allow construction equipment to crush the underdrain pipe or system as a result of the placement or compaction of the ATFDB.

Ensure a positive connection between the underdrain system and the ATFDB regardless of the sequence of operations in the Contract Documents.

308.13  Protection of the ATFDB.  The Department has not designed the ATFDB to be a haul road.  The Engineer will allow hauling units and other construction vehicles to operate on the ATFDB provided no significant displacement, breakup, or contamination occurs.  If the Engineer determines significant displacement, breakup, or contamination of the ATFDB is occurring, the Contractor shall stop operating hauling units and construction vehicles on the ATFDB.  Repair or replace all damage to the ATFDB, subbase, subgrade, or underdrains caused by the hauling units or construction vehicles at no additional expense to the Department.

Protect the ATFDB from fine material contamination at all times.

Provide adequate surface and subsurface drainage for the ATFDB, subbase, and subgrade at all times.

The Contractor may use a rubber tire paver if it does not damage the ATFDB, subbase, subgrade, or underdrains.  If damage occurs, cease paving and switch the rubber tire paver with a track mounted paver before restarting the paving.

When constructing asphalt concrete pavement on the ATFDB, allow the first course to cure overnight before placing the succeeding pavement courses.

308.14  Exposure to the Elements.  Place the next layer of pavement on the ATFDB within 40 days.

The Contractor may construct the ATFDB at any time if the temperature requirements of this specification are met.  Following construction of the ATFDB, completely cover the ATFDB with the next layer of pavement before the atmospheric temperature falls below 35 °F (2 °C) for any period of time.  Remove and replace all damage caused to the ATFDB, subbase, subgrade, or underdrains by the exposure to temperatures below 35 °F (2 °C) at no additional expense to the Department.

308.15  Method of Measurement.  The Department will measure the accepted quantities of Asphalt Treated Free Draining Base by the number of square yards (square meters).  The Department will measure the width as the width of the asphalt treated free draining base shown on the typical sections of the plans and additional widening where called for, or otherwise directed in writing by the Engineer.  The Department will measure the length horizontally along the centerline of each roadway or ramp.

308.16  Basis of Payment.  The Department will pay for accepted quantities, complete in place, at the contract price as follows:

Item           unit                                Description

308             Square Yard                     Asphalt Treated Free Draining Base
                       (Square Meter)